Technological improvements in semiconductor processing have led to a substantial increase in the number of transistors fabricated on a single integrated circuit. Along with an increase in the number of transistors also comes an increase in the amount of power dissipated by the integrated circuit. In an effort to reduce power dissipation and consumption, engineers have reduced the voltage level of the power supplies in such integrated circuits, from the traditional 5 volts to about 3.3 volts. This trend is expected to continue. Some current integrated circuits, for example microprocessors, operate at least a portion of their circuitry voltages below 3.3 volts. It is expected that more and more integrated circuits will be operated at power supply voltages below 3.3 volts.
Many integrated circuits are increasingly using mixed signal circuits (e.g. digital and analog) to perform various functions, such as voltage or current controlled oscillators. In addition, other circuits such as D/A (digital-to-analog) converters and multipliers may be employed in integrated circuits. Non-volatile memories, such as flash memories, include a digital portion for reading and accessing data and an analog portion for erasing. These designs generally require a reference current which is relatively stable across a range of operating temperatures and power supply voltages. With the increasing use of low-level power supply voltages, it is even more difficult to provide a needed stable current reference.
Accordingly, there is a need for a current reference which provides stable current over a range of operating temperatures and power supply voltages for use in integrated circuits.